Case mill having outwardly tapering flow path

ABSTRACT

A cage mill having a plurality of counter-rotating cages in which the path followed by the material being comminuted expands in the radially outward direction of the mill at an included angle from about 15* to about 30* . The cages comprise axially spaced end ring portions and axial bars extending between the end ring portions, the end ring portions of each cage outwardly from the innermost one being spaced axially outward beyond the ends of the axial bars of the cage adjacent thereto on the radially inner side thereof.

United States Patent [191 Stephenson et al.

(4 1 Nov. 13, 1973 1 1 CASE MILL HAVING OUTWARDLY TAPERING FLOW PATH [75] Inventors: Earle W. Stephenson, Latrobe, Pa.;

James G. Newberry, Lakeland, Fla.;

- Robert C. Hazzard, Mt. Vernon,

Ind.

[73] Assignees: Kennametal lnc., Latrobe, Pa.;

International Minerals & Chemical Corporation, Libertyville, Ill.

[22] Filed: Apr. 23, 1971 [21] Appl. No.: 136,983

Related [1.8. Application Data [63] Continuation of Ser. No. 847,988, Aug. 6, 1969,

abandoned.

[52] US. Cl. 241/187, 241/188 R [51] Int. Cl. B02c 13/20 [58] Field of Search 241/188, 187, 191

[56] References Cited UNITED STATES PATENTS 3,503,561 3/1970 Johnson 241/188 R 3,549,093 12/1970 Pallmann 241/188 R X 3,659,793 5/1972 Stephenson et a1 241/187 250,125 11/1881 Bennett 241/187 Primary Examiner--Othell M. Simpson Assistant Examiner-E. F. Desmond Attorney-Melvin A. Crosby [5 7] ABSTRACT A cage mill having a plurality of counter-rotating cages in which the path followed by the material being comminuted expands in the radially outward direction of the mill at an included angle from about 15 to about 30. The cages comprise axially spaced end ring portions and aitial bars extending between the end ring portions, the end ring portions of each cage outwardly from the innermost one being spaced axially outward beyond the ends of the axial bars of the cage adjacent thereto on the radially inner side thereof.

5 Claims, 2 Drawing Figures CASE MILL HAVING OUTWARDLY TAPERING FLOW PATH REFERENCE TO RELATED APPLICATION This application is a continuation of U.S. Pat. application Ser. No. 847,988, now abandoned.

This invention relates to cage mills and is particularly concerned with multi-row Cage mills.

Cage mills are well known and comprise one or more cages in the form of axially extending circumferentially spaced impact bars which are driven in rotation while material to be comminuted is fed into the center thereof so that as it moves radially outwardly the bars of the mill will impact against the material and reduce it in size. Such a cage mill may consist of a single row ofimpact bars or a plurality of rows of impact bars disposed different radial distances from the center of the mill and rotating at differential speeds with the differential speed preferably being obtained by rotating adjacent cages in respectively opposite directions.

Cage mills of the nature referred to are effective for comminuting, or reducing in size, the material passing therethrough but heretofore have had serious shortcomings in respect of abrasion of the cages, particularly when the cage mill is employed with relatively hard material and more particularly still when the material is supplied to the cage mill in the form of a slurry.

The present invention is particularly concerned with a cage mill constructed in such a manner that abrasion is held to a minimum within the cage mill thereby imparting longer life to the mill and making cage mills usable in situations where heretofore they have not been a practical instrument to employ for comminuting material.

In particular, the present invention relates to a multiple row or multiple cage mill having a plurality of telescopically arranged cages, each carrying axially extending circumferentially spaced bars with adjacent cages rotating in respectively opposite directions and so arranged that important supporting structural portions of the cages are protected from abrasion by the material passing through the cage mill.

Each cage in a cage mill of the nature referred to comprises the aforementioned bars and support members at the ends of the bars for supporting the bars and transmitting driving power thereto. The members at the ends of the bars and the parts connecting the members to the shaft by means of which the cages are driven in rotation are referred to as the structural parts of the cage mill and it is these parts, in particular, which tend to abrade away rapidly during the operation of the cage mill.

Forming of the bars of an abrasion resistant material is not uncommon but it is expensive and complicated toattempt to protect all the portions of the structural members of such a mill which will be subject to abrasion during operation of the mill. Most cage mills of the posed within the mill as to be protected from the abrasive effect of material passing through the mill.

A still further object of the present invention is the provision ofa multiple row cage mill in which improved comminuting of the material passing through the mill is obtained while at the same time the structural parts of the mill are protected from abrasion.

Another object of this invention is the provision of a A multiple row cage mill so constructed that the mill will run a substantially longer time on a set of cages than cage mills known heretofore.

'A still further object of the present invention is the provision of a cage mill having a high through put capacity and which operates more efiiciently than heretofore known cage mills.

The nature of the present invention will become more clearly apparent upon reference to the following detailed specification taken in connection with the accompanying drawings in which:

FIG. 1 is a perspective view showing an installation embodying a cage mill according to the present invention; and

FIG. 2 is a partial vertical section indicated by line II-II on FIG. 1.

Referring to the drawings somewhat more in detail, the mill in FIG. 1 comprises a base 10 having bearing supports 12 mounted thereon on which are mounted bearings 14 in which are journaled coaxial shafts l6 and 18. Each shaft carries a drive member such as a pulley and is driven in a respective direction of rotation by any suitable drive means such as an electric motor.

' Disposed between bearing supports 12 is housing 20 of the mill in which are disposed the telescopically arranged counter-rotating cages of the mill. A feed chute 22 is provided by which material to be comminuted is introduced into the mill through a lateral wall of housing 20 and in the region of the center of the innermost one of the cages of the mill. I

Referring to FIG. 2, the interior of the mill and the arrangement of the cages is shown in more detail. In FIG. 2 it will be seen that shaft 18 carries a hubmember 24 to which is bolted a relatively heavy disc-like plate 26, as by the cap screws 28. Disc like plate 26 extends radially outwardly and at its, outer end is connected to one end ofa set of axially extending bars, one of which is shown at 30. The bars 30 are uniformly circumferentially spaced about the outer marginal portion of plate 26 and extend axially in the housing 20 of the mill and have their ends opposite plate 26 interconnected by a ring 32. Bars 30 may be bolted or riveted or brazed or welded to plate 26 and ring 32 so that plate 26, ring 32, and bars 30 form a rigid structure.

Bars 30 in cross section may present a flat face on the leading sides thereof, or the bars may be round or have any other desired shape. Bars having flat leading faces are preferable for most materials and with the faces inclining somewhat forwardly toward the outside in order better to engage the material being treated.

Spaced inwardly from bars 30 is a second set of axial bars 34 having their one ends connected to plate 26 as by the heavy ring 36 and having their outer ends interconnected by another ring 38. Bars 34 are connected to rings 36 and 38 in any suitable manner and also form a rigid unit so that when shaft 1-8 rotates both of the cages made up of the bars 30 and 34 rotate in the same direction and in unison.

The other shaft 16, which is coaxial with shaft 18, also has a hub member 40 thereon with a disc-like plate 42, smaller than disc-like plate 26, connected thereto as by cap screws 44. Extending axially from the outer marginal portion of plate 42 are the axial bars 44 which are connected at their outer ends to a ring 46. Bars 44, which may be substantially identical with bars 30 and 34 are fixed to ring 46 and plate 42 in any suitable manner to provide a rigid structure.

Still another plate 48 is connected to ring 46 and extends radially outwardly therefrom to the side of ring 38. Connected to the outer marginal portion of plate 48 are axial bars 50 which are interconnected at their other ends by still another ring 52. Bars 50, similarly to bars 30, 34, and 44, are fixed to plate 48 and 52 in a suitable manner to form a rigid structure. Bars 44 and bars 50 form respective cages which are driven in unison by shaft 16 so as to rotate in the opposite direction to the cages formed by bars 30 and 34, and which are driven by shaft 18.

Hub 40 and shaft 16 may be protected by a resilient rubber-like coating 54 to inhibit damage that might occur thereto from the material fed into the mill through the opening 56 in the side wall which communicates with chute 22. Further, a deflector plate 58 may be stationary mounted in covering relation to the region of shaft 16 against whichthe material being fed into the mill would strike as it leaves chute 22.

The portions of the plates 26 and 48 and of rings 32, 36, 38, 46, and 52 at the ends of the bars of the cage mill and along at least parts of the radially inner and outer sides thereof may be protected by hard facing generally indicated at 60 if so desired.

The particular feature of the mill illustrated in the drawings which represents a substantial and particularly advantageous departure from the structures of known cage mills is the variation in the axial lengths of the respective cages. As will be seen, the bars of each cage are shorter than those of the next radially outward cage so that bars 44 of the innermost cage are the shortest and bars 30 of the outermost cages are the longest. This arrangement of the bars provides for a fan shaped flow of material being comminuted radially outwardly through the mill as indicated by the dot-dash ar rows 62. It will be appreciated that the structural elements of the mill, consisting of the aforementioned rings and plates, are disposed outside the principal flow path of the material being treated in the mill and are thus not subjected to abrasion as occurs in conventional known cage mill structures wherein all of the cages are of substantially the same length andstructural parts are disposed in the path of the material being treated.

As each bar impacts against material passing through the mill it will tend to break the particles of material so that as each particle is reduced by impact with a bar it covers a substantially greater cross sectional area of the flow path of the mill. If the cages are all made substantially the same length, according to known practices in the cage mill art, the efficiency of impacting of the bars against the material decreases in the radial outward direction so that the outermost bar of the cage mill may operate relatively inefficiently. With the cage mill according to the present invention, and wherein the bars increase in length in the radially outward direction of the mill, each bar has an opportunity to operate efficiently in impacting against the material and reducing the material to size. Thus, a high through put can be maintained and a high degree of efficiency of comminution will also be maintained.

The cages are arranged so as to be symmetrical about a central plane perpendicular to the axis of rotation so that the material being treated will fan out equal distances on both sides of the said central plane of the mill.

It has been mentioned that substantially longer life is obtained with a cage mill according to the present invention in addition to increased efficiency of comminution. For example, with semihard and abrasive material such as coal, a mill according to the prior art having all its cages substantially equal in length and, therefore, necessarily staggered somewhat axially, might run from 300 to 400 hours before it becomes necessary to replace structural parts of the mill. A cage constructed according to the present invention, on the other hand, can be expected to run from 1,500 to 3,000 hours before the cages require replacement or repair.

The cage mill according to the present invention can be used with dry materials or with slurries and is considered to have particular merit when used with slurries because of the rapid abrasion which occurs when abra sive material is passed through the mill in the presence of water. v

The mill is adapted to receive materials of various sizes, even up to 8 inch particle size where the material is not too difficult to break and will efficiently reduce the said material.

In one work operation material averaging about 15 mesh and consisting of ahigh degree of silica content can be passed through the mill at the rate of through put of about .200 tons an hour and the material will be reduced with a high degree of efficiency to a maximum sizeof about mesh. The material referred to, inasmuch as it has a high silica content, is extremely abrasive and, furthermore, is supplied to the mill in slurry form. This particular material has not heretofore been treated with success in a cage mill but is treated with a high degree of success in a cage mill constructed according to the present invention and characterized in the radially outwardly expanding flow path through the cages for the material being treated.

Modifications can be made in the structure illustrated within the scope of the appended claims.

What is claimed is:

1. In a cage mill having a housing with concentric counter-rotating cage means therein and means to introduce material to be comminuted into the innermost one of said cage means so that material will pass radially outwardly' through the cage means duringoperation of the mill; each said cage means comprising axially spaced end ring portions and axial bars extending between and rigidly fixed to said end ring portions in circumferentially spaced parallel relation, each said axial bar having a substantially flat and generally radial leading face for impacting against the material passing through the mill, said axial bars for the respective cage means increasing in length progressively from the innermost cage means to the outermost cage means, the axial central planes of said cage means being substantially coplanar, both of the said end ring portions of each cage means outwardly from the innermost one thereof being spaced axially outwardly a substantial distance beyond the ends of the said axial bars of the cage means adjacent thereto on the radially inner side thereof whereby the flow path through the mill for the material expands axially in the radially outward direction to a degree such that a minimum amount of the material passing through the mill impinges against the axially inner sides of said end ring portions.

2. A cage mill according to claim 1 in which said end ring portions of said cage means define a path for material being treated which widens in the axial direction of the mill substantially uniformly in the radially outward direction at an included angle between the sides of the flow path being at least about 30.

3. A cage mill according to claim 1 in which each said end ring portion has a corner at the axially inner edge of the radially outer periphery, the said corners of all of the said end ring portions at each end of said cage means when the cage means are viewed in cross section being disposed in substantially one and the same straight line.

4. A cage mill according to claim 1 in which said axial bars are welded to said end ring portions.

5. A cage mill according to claim 1 in which said axial bars are all about equal in radial extent when viewed in the circumferential direction of said cage means and the radial spacing between the axial bars of one cage means and the axial bars of an adjacent cage means is not over about one-half the radial extent of a said axial bar. 

1. In a cage mill having a housing with concentric counterrotating cage means therein and means to introduce material to be comminuted into the innermost one of said cage means so that material will pass radially outwardly through the cage means during operation of the mill; each said cage means comprising axially spaced end ring portions and axial bars extending between and rigidly fixed to said end ring portions in circumferentially spaced parallel relation, each said axial bar having a substantially flat and generally radial leading face for impacting against the material passing through the mill, said axial bars for the respective cage means increasing in length progressively from the innermost cage means to the outermost cage means, the axial central planes of said cage means being substantially coplanar, both of the said end ring portions of each cage means outwardly from the innermost one thereof being spaced axially outwardly a substantial distance beyond the ends of the said axial bars of the cage means adjacent thereto on the radially inner side thereof whereby the flow path through the mill for the material expands axially in the radially outward direction to a degree such that a minimum amount of the material passing through the mill impinges against the axially inner sides of said end ring portions.
 2. A cage mill according to claim 1 in which said end ring portions of said cage means define a path for material being treated which widens in the axial direction of the mill substantially uniformly in the radially outward direction at an included angle between the sides of the flow path being at least about 30*.
 3. A cage mill according to claim 1 in which each said end ring portion has a corner at the axially inner edge of the radially outer periphery, the said corners of all of the said end ring portions at each end of said cage means when the cage means are viewed in cross section being disposed in substantially one and the same straight line.
 4. A cage mill according to claim 1 in which said axIal bars are welded to said end ring portions.
 5. A cage mill according to claim 1 in which said axial bars are all about equal in radial extent when viewed in the circumferential direction of said cage means and the radial spacing between the axial bars of one cage means and the axial bars of an adjacent cage means is not over about one-half the radial extent of a said axial bar. 